Scientists have discovered that a detectable increase in the blood content of superficial mucous membrane occurs proximate cancerous and precancerous lesions in the colon relative to the blood content of healthy tissue as described in, for example, R K Wali, H K Roy, Y L Kim, Y Liu, J L Koetsier, D P Kunte, M J Goldberg, V Turzhitsky and V Backman, Increased Microvascular Blood Content is an Early Event in Colon Carcinogenesis, Gut Vol. 54, pp 654-660 (2005), which is incorporated by reference herein. This phenomenon is referred to as early increase in blood supply (EIBS).
Relying on this phenomenon, it is known that it is possible to predict an area of potential abnormality based on early increase in blood supply (EIBS) in the area of abnormality. Further, it has been discovered, that by using a probe applying collimated light to an area of interest, and detecting the amount of absorbed and reflected light it is possible to provide information to a clinician to guide an endoscope to detect a possible abnormality in vivo without an invasive procedure. Such techniques have been described for example in U.S. patent application Ser. No. 11/937,133 filed on Nov. 8, 2007, entitled “Blood Content Detecting Capsule”, assigned to the assignee of the present invention, which is incorporated by reference herein.
Typically, optical blood content detection relies on measuring the amount of light reflected from and interacted with the tissue mucosa back into the blood content detector. Because systems rely on measuring the amount of reflected light, the accuracy of the measurements are greatly impacted if the blood content detector and the spectroscope used to analyze the reflected light are not properly calibrated.
Various techniques exist for calibrating endoscopes. However, traditionally such calibration techniques have required the use of a special-purpose light source that emits light at a known wavelength and at a known intensity. Similarly, EIBS calibration techniques have been proposed wherein the intensity of the reflected light is calibrated utilizing a white diffuser panel. Such techniques are described, for example, in M. P. Siegel et al. Applied Optics, Vol. 45, Issue 2, pp. 335-342 (2006), which is incorporated by reference herein.
However, these proposed calibration techniques that are based on white light diffusion fail to address the fact that spectroscopes, used to perform spectral analysis during a blood content measurement are subject to inaccuracies often due to the misalignment of wavelength measurement values for the incident light. Such misalignments may occur due to inconsistent production variations, environmental changes, e.g., temperature and humidity, or variations due to use over time.
Other known techniques that employ wavelength calibration, however, require special-purpose calibration lights at significant costs and are limited to wavelength correction and cannot be utilized for intensity correction. Calibration of optical blood content detectors is further complicated by the fact that blood content detection relies on collecting light reflected from and interacted with the underlying tissue entering the detector at predetermined angles. In particular, it has been found that light reflected at, for example, at around 15 degrees with respect to the surface of living tissue aides in reducing the reflections. Because of this requirement, reliance on a special-purpose light for calibration is difficult because of the inability to ensure that transmitted calibration light is actually entering the blood content detector probe at the desired angle.
Accordingly, a need exists for an improved calibration technique for calibrating a blood content detector without reliance on special-purpose lights or other extraneous equipment in order to maintain a high level or improve the accuracy of blood content detector measurements.